change_property of object cannot change img_name

[NikkiBouman]

Describe the bug
I am trying to change the image of the object that is being carried as soon as it gets dropped (for example: square when picking up, circle when being put on the ground). I can change every property (for example "is_movable" can be set to False), except for the "img_name".

To Reproduce
I have my own custom action from the carrying objects together case.

class LowerObject(DropObject):
    def __init__(self, duration_in_ticks=0):
        super().__init__(duration_in_ticks)

    def mutate(self, grid_world, agent_id, world_state, **kwargs):
        # get robot and human ids
        global robot_id
        global human_id
        # get the robot and human
        robot = grid_world.registered_agents[robot_id]
        human = grid_world.registered_agents[human_id]
        # check who is carrying to get the object
        if human.is_carrying:
            obj = human.is_carrying[0]
        else:
            obj = robot.is_carrying[0]
        obj_id = obj.properties['obj_id']
        # change object properties
        obj.change_property("name", "broken")
        obj.change_property("img_name", "broken_light_box_human.png")
        obj.change_property("is_movable", False)
        kwargs["object_id"] = obj_id
        return super().mutate(grid_world, agent_id, world_state, **kwargs)

Expected behavior
At properties, the "img_name" should change to "broken_light_box_human.png". However, it does not change.

[NikkiBouman]

I fixed it by adding the following three lines:

            elif property_name == "img_name":
                assert isinstance(property_value, str)
                self.custom_properties["img_name"] = property_value

Into the change_property function of env_object.py. Probably not how it's supposed to be fixed, but it works

[thaije]

Hi Nikki,

I tried to reproduce this issue in various conditions and this is what I figured out:

Changing an image of an agent that already had an image (img_name set when you added your agent in your scenario file with factory.add_human_agent..) works in the manner that you described. However, there are some reasons why it could fail:

• The object/agent didn't have an img_name set on creation, and as such doesn't have the img_name property. In that case, use the add_property() function instead.
• The path to the image is not correct.

I will add an exception in the case that change_property() is called for a property that doesn't exist (yet).